The present invention relates to the construction of a ball or globe valve, particularly for use in shutting off pipelines and the like. Ball valves are known generally. They have several advantages. Among those advantages are their relative economy of manufacture and relatively little requirement for maintenance. When ball valves are used in high pressure lines, such as gas and oil transmission lines, one of their disadvantages becomes apparent. In order to maintain an effective seal such high pressure lines require a significant force between the ball seal and the valve seat. Opening or closing a standard ball valve by rotating it with respect to its housing promotes failure of the seal, whether the seal is carried by the ball or by the seat. The rubbing motion of the ball with respect to the seat tends to cause the seal to tear. When the seal fails the pipeline must be shut down and the valve entirely disassembled to permit replacement of the seal and the seat.
Various attempts have been made to provide closure members of the ball valve type in which the closure member moves in a direction axial to the seat to retract the seal before any angular movement. The inventor's existing U.S. Pat. No. 4,634,098 is one such example as are U.S. Pat. No. 2,577,725; German 1,122,788; France 2,383,369 and European patent A-107 868.
U.S. '725 and German '788 teach ball valves eccentrically mounted in a yoke which pivots. In these arrangements, however, the initial axial movement is accompanied by a rotational movement. French '369 and European '868 disclose ball valves having operating means whereby the closure member may be sequentially rotated and translated. However, those valves still require that the pipeline be shut down and the valve be completely disassembled in order to repair or inspect the seat.
The inventor's previous invention solved this problem first, by providing an inspection port in the housing for inspection, repair, or replacement, of the seal and second, by means of a concentric shaft system in which one shaft served to rotate the ball valve and the other shaft worked through means of a sliding block and an eccentric to cause translation of the seal in and out of the seat independent of angular motion. This previous embodiment required a pair of driven concentric shafts on one side of the ball valve, the top, and a second pair of slave concentric stub shafts diametrically opposite, on the bottom, joined by a slave arm. This slave arm assembly and its co-operation with the two eccentric shaft and slider assemblies yielded a structure which was relatively complicated and expensive to manufacture. Furthermore, retraction of the seal with respect to the valve seat was limited to twice the eccentric as achieved by rotation of one of the co-axial shafts 180.degree. with respect to the other co-axial shaft. This in turn limited the closure pressure that could be achieved to that which could be transmitted through the handle in one-half turn.